The use of X-rays in medical diagnosis has been known for many years. According to conventional techniques, an X-ray image is recorded on a silver halide X-ray film compressed between intensifying phosphor screens in a cassette. The X-ray film, on which the X-ray image has been recorded, is taken out of the cassette, fed into a developing machine and subjected to a development process which is comprised of a series of developing, fixing, washing and drying steps. The X-ray image is thereby developed into a visible image.
Particulars of the radiographic processes are described, for example, in Radiographic Photography by D. N. Chesney and M. O. Chesney, Blackwell Scientific Publications, Oxford, 1965, Radiographic Processing by D. H. O. John, Focal Press, 1967, or numerous other publications and patents in the field.
Techniques for reading out an X-ray image recorded, as described above, on the X-ray film and converting the image into an electric signal (image signal) by using a film digitizer have heretofore been known. Once the image signal is available, it may be stored, retrieved, processed and then reproduced into a visible image in any of the various ways offered by the digital image processing apparatus suitable for the digitization of photographic images, such as described, for example, by M. Gonoda in Computed Radiography Utilizing Scanning Laser Stimulated Luminescence, Radiology, September 1983, p. 833. Apparatus particularly useful for the digitization of conventionally produced X-ray images are commercially available under the trade names of "TRUSCAN" manufactured by Truvel Corp., "300A Computing Densitometer" manufactured by Molecular Dynamics, and "Laser Scanner KFDR-S" manufactured by Konica Corp.
U.S. Pat. No. 4,306,290 discloses means for digitizing a processed photographic film.
U.S. Pat. No. 4,755,447 discloses a wide-dynamic-range latitude silver halide film to be used with X-ray intensifying screen exposure and subsequent digitization and computer enhancement of the images produced thereon.
U.S. Pat. No. 5,237,358 discloses an apparatus for processing and digitizing a radiation image which comprises a) an automatic developing machine for carrying out a developing process on a silver halide photographic film, on which a radiation image has been recorded as a latent image, while said silver halide film is being passed through said automatic developing machine, and b) a film digitizer, which is connected to said automatic developing machine so that it may directly receive said silver halide film after it has been fed out of said automatic developing machine, said film digitizer photoelectrically reading out said radiation image from said silver halide film, which has been converted into a visible image during the developing process, and thereby generating an image signal representing said radiation image.
EP 452,570 discloses an apparatus for automatically processing, scanning and digitizing an exposed X-ray film comprising a) an automatic processing part in which said exposed X-ray film is processed to form an analog image on said film and b) a scanning/digitizing part in which said analog image is scanned and digitized, wherein the processing part and the scanning/digitizing part are directly linked, without any intermediate film storage means.
All these references disclose digitization of photographic images obtained by conventionally processing of image-wise exposed silver halide photographic films, that is developing, fixing, washing and drying of image-wise exposed silver halide photographic films. Image formation by conventional processing of photographic films requires a processing time (dry to dry) of at least 30 seconds. Film readout time must be added to processing time, thus giving a total time of not less than 45 seconds for processing and digitizing a photographic image. Digitization is effected by scanning the surface of the processed photographic film with a lamp located on one side of the film and collecting the light, which has passed through the film and is modulated in accordance with the image recorded on the film, with a radiation-sensitive sensor located on the side opposite to the lamp with respect to the film. Since, however, conventionally processed photographic images are characterized by different scattering of the scanning light crossing the film depending upon the optical density of the image (i.e., low light scattering in the unexposed image areas and high light scattering in correspondence of high optical densities), and light detected by the radiation-sensitive sensor can vary upon the scanning and collecting means due to light scattering, the image signal obtained by the digitization process does not perfectly represents the image information recorded on the photographic film and the image quality of the visible radiation image thus reproduced cannot be kept high. Additionally, present methods of processing and digitizing conventionally produced photographic films represent inconvenient procedures which require considerable time and labor.